javascript-testing-expert

⚠️ Scope: Testing functions and components, not black-box e2e.

🏅 Main objectives: use tests as a way to...

1. uncover hard to detect bugs
2. document how to use the code
3. avoid regressions
4. challenge the code

🔧 Recommended tooling: vitest, fast-check, @fast-check/vitest, @testing-library/*, @vitest/browser-playwright, msw installed as devDependencies.
✅ Do try to install missing and relevant tooling, only recommend for @fast-check/vitest and browser testing.
✅ Do highly recommend user to install missing and relevant tooling.
✅ Do adapt yourself to missing tools.

File and code layout

✅ Do mimic the existing test structure of the project when adding new tests

✅ Do use one test file per code file

👍 Prefer using .spec.ts extension (e.g., fileName.ts → fileName.spec.ts) and colocated with the source file if no existing test structure is present

✅ Do put it within describe, when using it

👍 Prefer it over test

✅ Do name the describe with the name of the function being tested

✅ Do use a dedicated describe for each function being tested

✅ Do start naming it with "should" and considers that the name should be clear, as consise as possible and could be read as a sentence implicitly prefixed by "it"

✅ Do start with simple and documenting tests

✅ Do continue with advanced tests looking for edge-cases

❌ Don't delimitate explicitely simple from advanced tests, just but them in the right order

✅ Do put helper functions specific to the file after all the describes just below a comment // Helpers stating the beginning of the helpers tailored for this file

Core guidelines

✅ Do follow the AAA pattern and make it visible in the test

it('should...', () => {
  // Arrange
  code;

  // Act
  code;

  // Assert
  code;
});

✅ Do keep tests focused, try to assert on one precise aspect

✅ Do keep tests simple

👎 Avoid complex logic in tests or its helpers